A boost converter has been known that boosts the voltage of an input power source by applying a duty drive to a switching element for switching cycles, and by using an inductor, to output the boosted voltage (see, for example, Patent Documents 1 and 2). This boost converter includes the inductor having one terminal connected with the input power source, the switching element connected between the other terminal of the inductor and the ground terminal, and a diode connected between the other terminal of the inductor and the output terminal of a load side.
In the boost converter, a controller controls the duty drive of the switching element based on the average value of a current flowing into the inductor during the switching cycle. Specifically, the controller applies the duty drive to the switching element, based on a duty command value calculated so that a command value for a current to be flowing into the inductor is equivalent to the average value of the current flowing into the inductor during the switching cycle.
When the switching element is turned on, the current flowing into the inductor from the input power source side does not flow to the load side via the diode, but flows to the ground terminal side via the switching element. While the switching element is on, the current flowing into the inductor gradually increases. Next, when the switching element is switched from on to off, the potential of the other terminal of the inductor rises from virtually zero to a level equivalent to the output voltage of the output terminal, and the current flowing into the inductor from the input power source side does not flow to the ground terminal side via the switching element, but flows to the load side via the diode. While the switching element is off, the current flowing into the inductor gradually decreases from a peak value taken when the switching element has been switched from on to off. Therefore, by repeating on and off of the switching element, the voltage of the input power source can be boosted to be output from the output terminal to the load side.